The present invention relates to a novel combustor of gas turbine and, more particularly, to a gas turbine combustor made of an Ni base alloy having a high resistance to thermal fatigue.
Combustors of gas turbines are usually shaped by cold working from sheet materials which in turn are formed by hot working from ingot of alloy. The alloy used as the material of the gas turbine combustor, therefore, is required to have good hot workability and cold workability. The alloy must have also a high resistance to thermal fatigue because the combustor is subjected to repetitional heat cycles consisting of heating by the hot combustion gas and subsequent cooling.
The present inventors have found that alloys having large tensile reduction of area at room temperature exhibit superior cold workability and also that high resistance to thermal fatigue is exhibited by alloys which have high tensile proof stress, tensile reduction of area, creep rupture strength and creep rupture reduction of area at high temperature.
A heat-resistant Ni base alloy called "hastelloy X", consisting essentially of 0.1 wt % of C, 22 wt % of Cr, 9 wt % of Mo, 0.5 wt % of W, 1 wt % of Co, 19 wt % of Fe and the balance Ni, has been used most popularly as the material of the gas turbine combustors.
On the other hand, there is an increasing demand for higher performance of gas turbines. This in turn requires a rise of the temperature of the working fluid, i.e. the higher temperature of the combustion gas. In consequence, the inner cylinder of the gas turbine combustor, the temperature of which is not raised above 750.degree. C. in the conventional gas turbine, is heated up to a high temperature exceeding 750.degree. C. Unfortunately, however, the above-mentioned common material hastelloy X cannot provide sufficient resistance to thermal fatigue at such a high temperature.
Namely, the hastelloy X, which is an alloy having a superior strength at high temperature owing mainly to solid solution strenghtening by Mo, exhibits only a low tensile proof stress at high temperature region above 750.degree. C., and shows only small creep rupture strength and creep rupture reduction of area. The hastelloy X, therefore, cannot provide sufficient thermal fatigue strength as the material of combustors for modern gas turbines.
Japanese Patent Laid-Open No. 18315/75 discloses an austenitic alloy of solid-solution strengthening type, consisting essentially of not greater than 0.1 wt % of C, not greater than 1.5 wt % of Al, not greater than 1 wt % of Ti and/or Nb, not greater than 75 wt % of Co, not greater than 26 wt % of Cr, 8 to 40 wt % of W, 38 to 46 wt % of [1/5 (wt % Co)+(wt % Cr)+(wt % W)], not greater than 0.1 wt % of Mg, not greater than 0.1 wt % of B, not greater than 0.5 wt % of Zr, not greater than 1 wt % of Hf and the balance substantially Ni. This literature, however, does not disclose nor suggest at all the application of this material to gas turbine combustors, and fails to mention the thermal fatigue resistance which is an essential requisite for the gas turbine combustor materials which have to withstand severe condition of use, i.e. repetitional heat cycles consisting of heating by hot combustion gas and subsequent rapid cooling.